This invention relates in general to imaging, and more specifically to migration imaging systems employing overcoated migration imaging members having an overlayer of electrically conductive material.
Recently, a migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution has been developed. Such migration imaging systems are disclosed in copending applications Ser. No. 837,780, filed June 30, 1969, and Ser. No. 837,591, filed June 30, 1969. In a typical embodiment of the new migration imaging system an imaging member comprising a substrate, a layer of softenable material and photosensitive marking material is latently imaged by electrically charging the member and exposing the charged member to a pattern of activating electromagnetic radiation such as light. Where the photosensitive marking material was originally in the form of a fracturable layer at the upper surface of the softenable layer, the marking particles in the exposed areas of the member migrate toward the substrate when the member is developed by softening the softenable layer.
"Softenable" as used herein is intended to mean any material which can be rendered more permeable thereby enabling particles to migrate through its bulk. Conventionally, changing the permeability of such material or reducing its resistance to migration of migration marking material, is accomplished by heat or solvent softening. "Fracturable" layer or material as used herein, means any layer or material which is capable of breaking up during development, thereby permitting portions of said layer to migrate toward the substrate or to be otherwise removed. The fracturable layer may be particulate, semi-continuous, or continuous in various embodiments of the migration imaging members.
There are various other systems for forming such images, wherein non-photosensitive or inert, marking materials are arranged in the aforementioned fracturable layers, or dispersed throughout the softenable layer, as described in the aforementioned copending applications which also disclose a variety of methods which may be used to form latent images upon such migration imaging members.
Likewise, various means for developing latent images in the novel migration imaging system are known. Typical development methods include solvent wash-away; solvent vapor softening, heat softening and combinations of these methods, although any suitable means for migration developing the imaging member is intended to be included herein. In the solvent wash-away method, the layer of softenable material is typically substantially washed away, leaving behind an image pattern of migrated marking material on the substrate. In the heat or vapor softening modes, the softenable layer is softened to allow imagewise migration of marking material toward the substrate and the developed imaged member generally comprises the substrate having migrated marking particles near the softenable layer-substrate interface, with the softenable layer and unmigrated marking materials intact on the substrate in substantially their original condition.
Various methods and materials and combinations thereof have previously been used to fix unfixed migration images. For example, fixing methods and materials previously used are disclosed in copending applications Ser. No. 590,959, filed Oct. 31, 1966, and Ser. No. 695,214, filed Jan. 2, 1968.
Copending application Ser. No. 172, filed Jan. 2, 1970, discloses novel migration imaging systems using migration imaging members having one or more overlayers of material which enhance the imaging systems. Such overlayers may comprise another layer of softenable material, a layer of material which is harder than the softenable material layer, or a gelatin layer.
In new and growing areas of technology such as the migration imaging systems of the present invention, new methods, apparatus, compositions of matter, and articles of manufacture continue to be discovered for the application of the new technology in new modes. The present invention relates to a new and advantageous migration imaging system employing overcoated imaging members having an overlayer of electrically conductive material thereon.